1. Field of the Invention
The invention relates to a method and a device for shaping a workpiece.
2. Background and Related Art
Percussive shaping machines such as hammers and screw presses, in particular flywheel screw presses, are known for industrial forging of workpieces. Percussive shaping machines comprise a working region in which two tools are movable, generally in a straight line, relative to one another. The workpiece is positioned between the two tools, and is then shaped by the impact force or impact energy from the striking of the tools on the workpiece and the resulting shaping energy.
According to VDI-Lexikon “Produktionstechnik Verfahrenstechnik” [Manufacturing Process Engineering], Prof. Dr. Hiersig, Publisher, VDI-Verlag, 1995, pages 1107-1113, forging hammers may be subdivided into anvil hammers—which in turn are subdivided into drop hammers and double-acting hammers—and counterblow hammers. An anvil hammer comprises an anvil (or support) as a tool that is stationary with respect to the workpiece, and a striking hammer, or hammer for short, as a tool that is movable, generally vertically, with respect to the workpiece and to the anvil. A counterblow hammer comprises two striking hammers that are movable, vertically or also horizontally, with respect to one another and relative to the base or the hammer frame. The drives for the hammers of forging hammers are generally hydraulic or pneumatic. In the actual shaping or work procedure, both the hammer frame and the hammer drives of a forging hammer are relieved of the shaping force so as not to overload the forging hammer. For screw presses, the workpiece that is moved is generally referred to as a tappet. The tappet is moved by a spindle in a straight line toward the stationary tool. The drive of the spindle, and thus of the tappet, is provided by a drive motor and/or a flywheel as an energy store. Before striking the workpiece located on the stationary tool, the spindle or tappet is decoupled from the drive, and the kinetic energy imparted to the tappet is (partially) transformed into shaping energy (VDI-Lexikon, see above).
For automatic handling of workpieces during pressing or forging, the use of handling devices such as manipulators and industrial robots is known from VDI-Lexikon “Produktionstechnik Verfahrenstechnik,” Prof. Dr. Hiersig, Publisher, VDI-Verlag, 1995, pages 848, 849, and 1214. Such handling devices have grippers for grasping and temporarily holding workpieces, and insert the workpieces into or remove them from the forging machine. Manipulators are manually controlled motion devices which as a rule have distinct, process-specific controls or programs. Industrial robots are universally applicable automatic motion devices with a sufficient number of degrees of freedom, implemented by a corresponding number (5 to 6) axes of motion, and a freely programmable control for achieving practically any given motion trajectories of the workpiece within an area which the industrial robot can traverse or reach.
One problem with the use of such handling devices is the high impact forces from a percussive shaping machine, which during the shaping impact can impose significant stress and cause damage to the handling device when the handling device holding the workpiece is struck by the hammer or tappet. To solve this problem, DE 42 20 796 A1 and DE 100 60 709 A1 have proposed handling devices which can be flexibly positioned during the impact to damp the impact forces and vibrations transmitted from the workpiece to the drive, and which can be rigidly positioned during transport of the workpiece.
Automated handling of workpieces in forging processes with percussive shaping machines has not yet achieved widespread acceptance in actual practice. Instead, in practice the workpiece is still manually held in the forging hammer using a gripping tool, since appropriately trained operators control the correct handling of the workpiece when it is struck by the hammer along with the striking tool. After the hammer is reversed, the operator lifts the workpiece and places it back in the tool before the hammer strikes again with the next lift, or immediately places the workpiece in a depositing device.